1. Field of the Invention
The present invention relates to an electronic microscope apparatus having a function to measure an element image of a specimen.
2. Background Art
As a result of making semiconductor elements and magnetic head elements finer and smaller in size, such elements have a structure in which thin films of several nanometers are stacked in a region on the submicron order. In the development of elements, it is important to analyze the structure of such a minuscule region and an element distribution in such a region. Devices for performing elemental analysis include a characteristic X-ray spectrometer and an electron beam energy analyzer (also called an energy filter), which are attached to transmission electron microscopes (TEM) or scanning transmission electron microscopes (STEM) for observing and designating a minuscule region.
In a case where an element image with a good S/N is observed by using a characteristic X-ray spectrometer or an electron beam energy loss spectrometer, a method of improving the signal intensity by increasing the observation time is ordinarily used. However, if the observation time is increased, a specimen drift caused in the observation time causes a deterioration of the resolution of the element image. As a method for solving this resolution deterioration problem, a method described in JP Patent Publication (Kokai) No. 2002-56798 for example should be mentioned.
According to the method described in JP Patent Publication (Kokai) No. 2002-56798, in a case where an electron beam energy loss spectrometer is attached to a TEM, an energy filter image including a core loss (core electrons) (hereinafter referred to as “F1 image”), and energy filter images based on lower-loss energy electrons (hereinafter referred to as “F2 image” and “F3 image”) are obtained, as shown in FIG. 8. Also, an f1(t1) image, an f1(t2) image, . . . and an f1(tn) image are added up by observation at different times to obtain an F1 image. Similarly, an f2(tn+1) image, an f2(tn+2) image, . . . and an f2(t2n) image are added up to obtain an F2 image. Further, an f3(t2n+1) image, an f3(t2n+2) image, . . . and an f3(t3n) image are added up to obtain an F2 image. Thereafter, an image formed only of an F1 image background signal (hereinafter referred to as “BG image”) is computed by using the F2 image and the F3 image, and the BG image is subtracted from the F1 image to obtain an element image. As a computation method, a three-window method disclosed in “Electron Energy Loss Spectroscopy in the Electron Microscope” written by Egerton may be used.